An electric cable comprises one or more groups of twisted conductor wires. A group is conventionally constituted by two twisted-together conductor wires—in which case it is called a “pair”—but could equally well comprise more than two twisted-together conductor wires.
A helically-wound electric cable comprises a plurality of groups that are wound together to form a helix.
The term “cross-talk” designates electromagnetic interference between groups belonging to a given electric cable. The cross-talk phenomenon frequently gives rise to problems with data transmission.
In order to reduce cross-talk, it is known to twist the conductor wires together in helixes of pitches that differ from one group to another, in order to prevent the conductor wires of any given group interfitting between the conductor wires of other groups.
U.S. Pat. No. 6,318,062 describes a method of varying the twisting pitch within a pair. That method also serves to prevent the conductor wires being roughly parallel with one another along the cable by preventing the conductor wires of a given group interfitting between the conductor wires of other groups.
Document EP-A-1 174 886 also discloses a helically-wound electric cable comprising at least two groups wound together in such a manner as to form a group helix, each group comprising at least two twisted-together conductor wires, the pitch of the group helix varying along said cable.
Since the frequencies carried by helically-wound electric cables are increasing, it is nowadays necessary to further reduce the phenomenon of cross-talk.